The detecting performance of an airborne daytime star sensor for navigation is analyzed and a daytime star sensor prototype is researched. Mathematical models of Signal to Noise-Ratio(SNR) and contrast of a photoelectric imaging system in daytime under noises are established, and calculated results by different focal lengths and different apertures are compared to conclude the influence of system parameters on the detection results and the requirements of optical system. The conclusion shows that the proper relative aperture of optical system is 1/15. A daytime star sensor prototype for tracking stars of magnitude 3 is designed. Tracking images of the polestar from sunrise to noon are acquired by a ground experiment using a F/15 objective, and brightnesses and contrasts of star images at different time are compared. It shows that the contrast of star image has descended from 1. 55 at 5:00 a. M. To 1. 2 at 12:00 a. M. The minimal degree of modulation is more than 0. 03 by calculating with the prototype's parameters, which shows that the optical system with Φ70 mm and F/15 can satisfy the detecting requirements. The theoretic analysis and design is proved to be available, and the research can be a reference for developing of miniaturized and precise airborne daytime navigation star sensors.%理论分析和试验研究了机载导航白天星敏感器的探测性能,建立了白天观星的信噪比和调制度在噪声影响下的数学模型,对比了焦距一定,不同人瞳直径和入瞳直径一定,不同焦距情况下的计算结果.归纳了光学系统的性能要求及系统参数对探测效果的影响,得出光学系统相对孔径为1/15较为合适的结论.在此基础上提出了用于3等星全天时观测的白天星敏原理样机的光机及电子学处理总体方案.利用相对孔径为1/15的望远物镜进行地面实验,获得了对北极星从日出到正午的持续观测结果.对比不同时刻星点图像的亮度和对比度变化显示,随着太阳高度角增大,星点图像的对比度由上午5:00的1.55下降到正午12:00的1.2左右,据此换算出样机方案的探测性能指标.计算结果表明,采用口径为Φ70 mm,相对孔径为1/15的光学系统可满足对3等星的探测最小调制度为0.03的要求.实验表明,本文进行的理论分析正确,方案合理可行,可为小型高精度机载导航星敏感器的研制提供参考.
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